The present invention relates generally to location of opens in a conductive line of an insulated conductor, and more particularly, to a method for locating opens in the conductive line of the insulated conductor by monitoring a locator signal introduced into the conductive line.
A shielded cable is a conventional means of carrying telecommunications transmissions. A plurality of paired lines are bundled together in a shielded cable and surrounded by a conductive shield which in turn is surrounded by an insulative sheath. Each paired line of the shielded cable is capable of independently carrying a telecommunications signal. Shielded cables are generally effective telecommunications carriers, however, a type of fault termed an open can occasionally occur in the shield which interferes with the quality of the telecommunications transmissions. The open allows an increased coupling of extraneous voltages into one or more enclosed paired lines of the shielded cable from nearby sources, such as power transmission cables The open typically causes noise in the affected paired lines which is extremely disruptive to the clarity of the telecommunications signal sent over the paired line Therefore, it is desirable to locate and repair opens in telecommunications cables.
Since telecommunications cables are not always readily accessible, often being buried below ground, noninvasive methods are preferred for locating faults in telecommunications cables. Tone location methods are a noninvasive means for locating resistance faults in paired lines of telecommunications cables using an audible tone as a locator signal. One such effective method is taught by U.S. Pat. No. 5,995,588. However, the method is less effective for locating opens in the shield.
Accordingly, it is an object of the present invention to provide a method for effectively locating opens in a conductive line of an insulated conductor using a locator signal. In particular, it is an object of the present invention to provide a method for effectively locating opens in a conductive shield of a shielded cable using a locator signal. It is a further object of the present invention to provide a method for effectively locating opens in the shield of a shielded cable using a device which is fully portable in the field for expeditiously tracking relatively long lengths of the shielded cable. These objects and others are accomplished in accordance with the invention described hereafter.
The present invention is a method for locating an open in a conductive line of an insulated conductor surrounded by an insulative sheath. In accordance with a first embodiment, the insulated conductor is beneath an earthen surface. A locator signal and a carrier signal including synchronization of the locator signal are introduced into the conductive line of the insulated conductor at a transmission point. A ground current is capacitively transmitted from capacitive points along the conductive line across the insulative sheath through earth to a ground reference in response to the locator and carrier signals. The capacitive points are downstream of the transmission point and upstream of the open in the conductive line. The transmission point is positioned between the ground reference and the capacitive points.
A ground locator signal and a ground carrier signal are received in response to the ground current flowing through earth to the ground reference past a pickup positioned at a downstream point proximal to one of the capacitive points. The pickup has a first probe and a second probe spaced apart from one another along a pickup axis. The first and second probes are in electrical communication with earth at the downstream point to receive the ground current. The pickup axis is aligned substantially perpendicular to the longitudinal axis of the insulated conductor at the capacitive point and is positioned a proximal to the insulated conductor.
The ground locator signal has a real component and a quadrature component differing from the real component by a 90xc2x0 phase shift. The ground carrier signal has real synchronization and quadrature synchronization. The quadrature component, which is indicative of the open, is detected using the quadrature synchronization to exclude the real component. The pickup is incrementally repositioned at succeeding downstream points proximal to the insulated conductor and away from the transmission point. The open is located at a point on the insulated conductor proximal to a succeeding downstream point where the quadrature component exhibits an abrupt change. A resistance fault in the insulated sheath may also be located in accordance with the present embodiment at a point on the insulated conductor proximal to a succeeding downstream point where the real component substantially exceeds the quadrature component.
In accordance with a second embodiment of the present invention, the insulated conductor is on or above an earthen surface. A locator signal and carrier signal are introduced into the conductive line in substantially the same manner as recited above. A capacitive pickup is moved along the insulated conductor downstream of the transmission point and upstream of the open. A capacitive current is capacitively transmitted from capacitive points along the conductive line across the insulative sheath to the capacitive pickup in response to the locator and carrier signals. A capacitive locator signal and a capacitive carrier signal are received in response to capacitive transmission of the capacitive current from the pickup to an ungrounded common. The capacitive locator signal has a real component and a quadrature component and the capacitive carrier signal has real synchronization and quadrature synchronization. The quadrature component is detected using the quadrature synchronization to exclude the real component. The open is located at a point on the insulated conductor where the quadrature component exhibits a significant abrupt change.